It's important for diabetes to be diagnosed early so treatment can be started as soon as possible.

If you experience the symptoms of diabetes, visit your GP as soon as possible. They'll ask about your symptoms and may request blood and urine tests.

Your urine sample will be tested for glucose. Urine doesn't normally contain glucose, but glucose can overflow through the kidneys and into your urine if you have diabetes.

If your urine contains glucose, a specialised blood test known as glycated haemoglobin (HbA1c) can be used to determine whether you have diabetes.

Glycated haemoglobin (HbA1c)

In people who have been diagnosed with diabetes, the glycated haemoglobin (HbA1c) test is often used to show how well their diabetes is being controlled.

The HbA1c test gives your average blood glucose levels over the previous two to three months. The results can indicate whether the measures you're taking to control your diabetes are working.

If you've been diagnosed with diabetes, it's recommended you have your HbA1c measured at least twice a year.

However, you may need to have your HbA1c measured more frequently if:

  • you've recently been diagnosed with diabetes
  • your blood glucose remains too high
  • your treatment plan has been changed

Unlike other tests, such as the glucose tolerance test (GTT), the HbA1c test can be carried out at any time of day and doesn't require any special preparation, such as fasting. However, the test can't be used in certain situations, such as during pregnancy.

The advantages associated with the HbA1c test make it the preferred method of assessing how well blood glucose levels are being controlled in a person with diabetes.

HbA1c can also be used as a diagnostic test for diabetes and as a screening test for people at high risk of diabetes.

HbA1c as a diagnostic test

In 2011 the World Health Organization (WHO) recommended that HbA1c could also be used to help diagnose type 2 diabetes in people who aren't known to have the condition.

An HbA1c level of 6.5% (48mmol/mol) or above indicates type 2 diabetes.

Although there's no fixed point to indicate when someone has pre-diabetes, a UK expert group has recommended that an HbA1c level of 6-6.4% (42-47 mmol/mol) would indicate that a person has a high risk of developing diabetes.

You can read more about the HbA1c test on the Lab Tests Online UK website.

Glucose tolerance test (GTT)

A glucose tolerance test (GTT), sometimes known as an oral glucose tolerance test (OGTT), can show if your body is having problems processing glucose.

Before having the test, you'll be asked not to eat or drink certain fluids for 8-12 hours. You may also need to avoid taking certain medications before the test, as they may affect the results. 

A blood sample will be taken before the test and your blood glucose will be measured. You'll then be given a sweet glucose drink.

After drinking the glucose drink, your blood glucose will be measured again after two hours. As you will have a long time to wait between blood tests, you may want to take something to read or listen to.

Test results

The results of the GTT will show whether you have impaired glucose tolerance (IGT) or diabetes. This will be based on the amount of glucose in your blood both before and after drinking the glucose drink.

Blood glucose is measured in millimoles per litre, often written as mmol/l.

For someone without diabetes, the amount of glucose in their blood should be:

  • less than 6 mmol/l before the test
  • less than 7.8 mmol/l two hours after the test

If you have IGT, the amount of glucose in your blood will be:

  • 6-7 mmol/l before the test
  • 7.9-11 mmol/l two hours after the test

If you have diabetes, the amount of glucose in your blood will be:

  • more than 7 mmol/l before the test
  • more than 11 mmol/l two hours after the test

If your test results indicate you have IGT, you may be advised to make lifestyle changes, such as eating more healthily and taking more exercise. Medication to lower your blood glucose level may also be recommended.

If your results indicate you have diabetes, it is likely medication will be prescribed. This will lower your blood glucose level and help keep it under control.

Page last reviewed: 27/06/2016
Next review due: 27/06/2018